It is already known that an LIH manager restricts the functions of the control systems for example by activating an emergency operation function (LIH functions, Limp Home Function) or in the worst case scenario simply deactivates the relevant control systems. This maximum reaction to a fault in the control systems is initiated because the actual cause of the fault symptom is not known.
It is also known that fault symptoms of similar identification methods are combined in diagnosis methods. These methods have a Diagnostic Trouble Code, as set out in the ISO standard.
A method for the controlled operation of a device, in particular an internal combustion engine, in which fault symptoms are diagnosed, is known from DE 199 41 440 A1. Cross-influences from consequential faults can result from the fault symptoms, with the consequence that the actual system diagnosis of operating or control functions is highly complex and therefore difficult to analyze. Severe and lenient operating or control restriction requirements are first differentiated and evaluated when verifying cross-influences. The operating or control restriction requirements are then filtered such that no contradictions occur. After the cross-influences have been verified, a series of individual measures is authorized, possibly in combination with a plurality of measures, each of which is evaluated according to the severity of its intervention in the operation of the device. A matrix method is proposed for evaluating and analyzing the individual faults in the electrical diagnosis and the functional diagnosis. The matrices of the matrix are multiplied to produce a process plan. The process plan thereby takes into account temporal prioritization and the cross-influences of the diagnosed faults such that the device can be operated to perform to the maximum possible level.
A further fault diagnosis method is known from DE 197 23 097 C1. Here the mutual direct dependencies of the monitored operating functions are input in a matrix with a “1” or if there is no dependency with a “0”. With dependent faults a so-called dilemma or deadlock results, which indicates that two monitored malfunctions cause a mutual dependency. This means that consequential faults can be distinguished from standard faults. If it is possible to break the mutual dependency of the two malfunctions, the causal fault can be determined. This process is referred to as validation.